Glowing in the Dark

question 172

Multiple Choice

Glowing in the Dark
Have you ever wondered how glow-in-the-dark things actually glow in the dark? Most glow-in-the-dark items glow because of something called phosphorescence or photoluminescence. Phosphorescent items must be "charged" under a bright light before they actually glow in the dark. This charging process works because of a substance called phosphor.
When light from the sun or a lamp hits phosphor, the phosphor molecules absorb the light and become energized. As the phosphor molecules release the stored energy, they emit a dim light that is visible in the dark. The color of the light that they produce depends on the color of the dye added to the glow-in-the-dark item. Usually, green dye is added to the phosphors to make the light easier to see. Although any color can be used, the human eye sees green light most clearly in the dark.
There are also a few glow-in-the-dark items that do not need to be charged. Emergency exit signs, gun sights, and certain kinds of expensive wristwatches glow because of radioluminescence. In these items, the phosphor is mixed with a radioactive element called tritium. The radiation from the tritium provides energy to the phosphor. It is almost as if there are thousands of tiny lamps constantly shining on the phosphor. Because their phosphor is always energized, these radioluminescent items are always glowing.
One other kind of glow-in-the-dark item that does not require charging is the glow stick. Glow sticks do not need to be held under light and do not contain any radioactive elements. Instead, glow sticks glow using chemiluminescence. Glow sticks contain a fluorescent dye and a thin glass tube that contains a chemical. To activate a glow stick, you bend the plastic container, causing the glass to break. The chemical inside the glass then mixes with the dye. The combination of the chemical and the dye produces visible light.
Question: Why does the author mention "thousands of tiny lamps" in paragraph three?

• A)To link two different elements that are found in nature.
• B)To suggest that the radiation from tritium acts as if it were a lamp.
• C)To state that the light emitted from the phosphor is as bright as a lamp.
• D)To explain that a lamp must shine on tritium in order for it to glow.

---

Definitions:

Express Contract

A contract explicitly stated by the parties, either orally or in writing, detailing the terms clearly.

Contract Formed

refers to the creation of a legally binding agreement that arises when an offer by one party is accepted by another party, meeting the necessary legal requirements.

Unilateral Contract

A contract where one party makes a promise in exchange for the performance of a specified act by the other party, who is not obligated to perform.

Quasi Contract

An obligation imposed by law to prevent unjust enrichment, where no actual contract exists.